LDKBMWND parameter: Difference between revisions
m (Further clarification of the relationship between NUMBUF and LDKBMWND) |
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<dd>(version 7.4 and earlier) <var>[[NSERVS_parameter|NSERVS]]</var> plus 1. | <dd>(version 7.4 and earlier) <var>[[NSERVS_parameter|NSERVS]]</var> plus 1. | ||
<p>(version 7.5 and later) A minimum of ( 0.5 * <var>[[NUMBUF_parameter|NUMBUF]]</var> ).</p> | <p>(version 7.5 and later) A minimum of ( 0.5 * <var>[[NUMBUF_parameter|NUMBUF]]</var> ).</p> | ||
Before the value of LDKBMWND is adjusted or recalculated, the minimum size of NUMBUF must first be determined by this formula: | |||
<p class="code">NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)</p> | <p class="code">NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)</p> | ||
<p>If the current | <p>If the current value of NUMBUF exceeds this value and the value is a multiple of NLRUQ, no further adjustments to NUMBUF are made.</p> | ||
Following that, if a value for LDKBMWND is specified in CCAIN and that value is greater than 0.5*NUMBUF, the value can still be adjusted: | Following that, if a value for LDKBMWND is specified in CCAIN and that value is greater than 0.5*NUMBUF, the value can still be adjusted: | ||
<ul> | <ul> | ||
Revision as of 17:10, 6 May 2016
# of pages in DKBM-BTB anticipatory write window
Summary
- Default value
- (version 7.4 and earlier) NSERVS plus 1.
(version 7.5 and later) A minimum of ( 0.5 * NUMBUF ).
Before the value of LDKBMWND is adjusted or recalculated, the minimum size of NUMBUF must first be determined by this formula:
NLRUQ * ((NSERVS + NSUBTKS) * MAXOBUF + 15)
If the current value of NUMBUF exceeds this value and the value is a multiple of NLRUQ, no further adjustments to NUMBUF are made.
Following that, if a value for LDKBMWND is specified in CCAIN and that value is greater than 0.5*NUMBUF, the value can still be adjusted:
- The final value must be an even multiple of NLRUQ
- The final value must not be greater than NUMBUF minus the total number of buffers that might possibly be open at any one time:
NUMBUF - (((NSERVS+NSUBTKS)*MAXOBUF)+14)*NLRUQ
- Parameter type
- System
- Where set
- On User 0's parameter line by system manager
- Related products
- All
- Introduced
- Model 204 V6.1 or earlier
Description
An anticipatory write window that starts writes for any modified buffers that enter the window.
When an anticipatory write for a modified buffer completes, the buffer is immediately reusable.
High values of LDKBMWND might unnecessarily increase the number of writes done (measured by the DKWR statistic). Low values might cause excessive waiting for buffers (measured by the DKSWAIT statistic).
Refer to Disk buffer monitor statistics and parameters and Disk buffers and Model 204 storage for more information about anticipatory write windows and disk buffers.